Hypothetical Curtiss P-36N — A P-40N Returning to Radial Power

[_PabloSniper_]

Hypothetically, it's 1943. Allison is struggling to supply enough V-1710 engines, so Curtiss decides to use the successor to the R-1830, the Pratt & Whitney R-2000, already in service on the DC-4.
Basically, this would be a P-40N powered by a 1,450 hp radial engine.
P.S.: The R-1830 used in the P-36 weighed approximately 620 kg (1,367 lb), while the R-2000 weighs approximately 720 kg (1,587 lb).

 

[MiTasol]

If my memory is correct there was a close cowled P-36 which had a significant increase in performance. That installation using the R-2000 in a P-40N airframe may have had a quite respectable performance given the P-40s superior roll rate.

 

[Greg Boeser]

Curtiss already had a number of P-40 successors they were working on to compete with the P-47 and P-51. Why would they divert R&D for a retrograde design?

 

[SaparotRob]

Curtiss already had a number of P-40 successors they were working on to compete with the P-47 and P-51. Why would they divert R&D for a retrograde design?

It was kinda' their thing.

 

[Jugman]

If my memory is correct there was a close cowled P-36 which had a significant increase in performance. That installation using the R-2000 in a P-40N airframe may have had a quite respectable performance given the P-40s superior roll rate.

P&W had a Curtiss Model 81A (probably a Tomahawk II airframe) that they modified with a two-stage R-1830. Between July and October 1943 It achieved a top speed of 388mph @ 25,000ft on 1015hp. Speed at sea level was 315mph on 1200hp. Fit and finish were probably some what better than what could be expected from Curtiss and it didn't have combat equipment.

 

[RpR]

Pratt&Whiney installed a larger engine into a P-36 on their own time and money.
It out performed the P-40 at the time but Curtiss with their CF administration refused it.

 

[tomo pauk]

Pratt&Whiney installed a larger engine into a P-36 on their own time and money.
It out performed the P-40 at the time but Curtiss with their CF administration refused it.

What was that 'larger engine'?

 

[RpR]

I do not have the book here that tells the tale of that set-up, I will look when I get to where the book is.

 

[MIflyer]

The R-2000 was not considered to be the next development after the R-1830. Rather, it was an R-1830 with cylinders that were a little longer. The reason they built it for the C-54 was not for more HP but because aviation was in the process of switching from the 73 octane of the 1930's to the 87 octane and 100 octane of the later years. Douglas could not be sure that a DC-4 or C-54 would only be operating out of airfields that had the higher octane fuels. So by slightly enlarging the R-1830 they had an engine that would still provide the required HP even with lower grade fuels.

As for the R-1830 with a two stage supercharger, you are talking the same engine as used on the F-4F, a fine aircraft that had as good or even better maneuverability than the P-36 (as USN pilots discovered over Casablanca) but also one that was not what you'd call a speed demon.

The next step up in HP in a radial would have been the Wright R-2600, but it weighed almost 500 lb more than an R-1830.

 

[YavorD]

Curtiss radial engine project for a P-36 successor was XP-42.
Three years later P-60 variants, XP-60C,E, powered by R-2800 radial engine emerged. XP-62 and XF14C were powered by R-3350 variants. Anyway, very different aircraft with a little connection to the P-36/40 ancestors.
Pratt & Whitney installed a R-1830 with a two-stage mechanically driven supercharger (very much alike R-1830-86 in F4F-3 & 4, and FM-1) in a production P-40 airframe.

Best regards,
Yavor

P.S. The very last Curtiss NAVY fighter project reaching a prototype stage was XF15C : R-2800 + J36.

 

[MiTasol]

Pratt&Whiney installed a larger engine into a P-36 on their own time and money.
It out performed the P-40 at the time but Curtiss with their CF administration refused it.

That is the one I was thinking of.

 

[MiTasol]

What was that 'larger engine'?

R-1830.

 

[Shortround6]

A non-starter.
The 1450hp disappears real fast after take-off Power starts falling off over 1000ft.
Even in high gear it was good for 1100hp at 16,000ft.
With the drag of the radial engine things are not looking good.
The R-1830 and R-2000 never got WEP ratings.

1943 the Allison engines used in the P-40Ns could make over 1400hp using WEP from sea level to around 10,000ft (climbing or level high speed flight made a difference.)

I will note that the P&W testbed aircraft described by Jugman in post #5 had no guns (not even .30 cal) and was flown at a gross weight of 7100lbs. It was estimated that a 'service version' would gross over 8,300lbs clean with guns/ammo and protective equipment.
The test bed aircraft did not have armor/BP glass or self sealing tanks.

Using the R-2000 engine in a specialty fighter bomber might work, as a fighter to try for air-to-air at over 10,000ft (?) you are going to be in trouble. C-54 engine limits were 50in MAP in low gear and 41.5in in high gear. Change-over was between 12,000ft and 14,000ft.

A 1943 airplane will have better cowl and exhaust than the 1939 P-36. question is it as good as the Allison P-40? Or even close?

 

[GrauGeist]

Curtiss tested a few radials in their XP-60 project

The XP-60A-1 was planned to have an R-2800-18 installed, but was canceled.

The XP-60C had an R-2800-53 installed.

The XP-60E had an R-2800-10 installed.

Following the various spin-offs of the P-40 is like going down a rabbit hole. So basically, the P-60 derived from the P-53, which came from the P-46, which was developed from a P-40.

 

[Greg Boeser]

The Luftwaffe encountered scores of P-46s in North Africa.

 

[cherry blossom]

Good point by SR6 about the loss of power with altitude but if we are seriously in what if territory, we could fit a R-2800 supercharger, like the DB603 supercharger in late DB605s and the Vulture as the first stage of the Merlin 60, and add water injection. As we are only adding air rather than fuel we may not need to worry about cooling but we will need to strengthen some things. We might need to use water/methanol for military power and above, forcing us to use large tanks as on the Ki-100.

 

[Shortround6]

Good point by SR6 about the loss of power with altitude but if we are seriously in what if territory, we could fit a R-2800 supercharger, like the DB603 supercharger in late DB605s and the Vulture as the first stage of the Merlin 60, and add water injection. As we are only adding air rather than fuel we may not need to worry about cooling but we will need to strengthen some things. We might need to use water/methanol for military power and above, forcing us to use large tanks as on the Ki-100.

Interesting but it adds time (development) to the scenario.
Number of weeks/months needed to adapt the R-2800 supercharger (even the one out of a B-26 bomber) to the smaller engine would be?
Trying to design/adapt parts to make a two-stage supercharger is going to take more time.

Cooling with radials (air cooled) is hard. Water injection helps (more development time?). But at 20,000ft you have about 1/2 cooling (air mass flow) at the same speed at sea level.
Yes adjustable flaps help with air flow and high speed doesn't need open flaps but climb may.

DB 603 supercharger on DB 605 cost around 50hp at sea level (nothing is free).
You add air so you can burn more fuel. Problem is balancing the desired fuel burn at altitude to the available cooling.

Problem with the P-40 in 1943 (even in Jan) is that it is seen as a short-term solution. Except at Curtiss. Curtiss was desperate to try anything as the P-46, P-53, P-55 and P-60 (various versions) all failed or in Jan 1943 were still trying to be developed. Orders extending into 1944 were diminishing.
Not sure when the P-40Q program started on paper. Granted the P-40Q used the Allison engine but Curtiss needed a competitor to the P-47 and P-51 and other prototypes/programs that offered much better performance than the P-40 air frame.
A quicky substitute engine to get around a shortage of Allisons is one scenario, doing even several months of supercharger R & D is another.

 

[tomo pauk]

Impeller diameter on the 1-stage supercharged R-1820 and on the 1-stage supercharged R-2800 A & B series was the same - 11 in. It rotated (max) at 8.47 times the crankshaft speed on these R-1830s, and 9.89 times the crankshaft speed on these R-2800s. That is the mainstream versions, as found on the military aircraft of the day - 1941 to 1944-ish. A problem with the impellers on the P&W and most radials of the day were the straight impeller blades; it took P&W until well into 1944 to start making the impellers with curved blades. Cluttered intakes of the radials of the time - P&W engines included - were bad for airflow, inducing the losses at any altitude. Turning the inefficient S/C much faster eats up a lot of engine power and heats the charge too much - the things not wanted on any engine, not only the engine powering the military aircraft.

Unlike that, the impeller of the DB 603A was bigger than what the DB 605A had - diameter of 295mm vs. 265mm (11.61 in vs. 10.43 in), and the impeller was of the more modern shape, and the intake was probably as uncluttered as possible. No wonder the effects of the altitude power of the 605AS and the subsequent engines were that good.

So just switching the supercharger will not do anything for the R-1830, IMO. A more modern supercharger will help a lot, but that was not in the P&W cards well until the R-1830 was relegated into the 3rd league as far as the military engines go.

 

[Howard Gibson]

Hypothetically, it's 1943. Allison is struggling to supply enough V-1710 engines, so Curtiss decides to use the successor to the R-1830, the Pratt & Whitney R-2000, already in service on the DC-4.
Basically, this would be a P-40N powered by a 1,450 hp radial engine.
P.S.: The R-1830 used in the P-36 weighed approximately 620 kg (1,367 lb), while the R-2000 weighs approximately 720 kg (1,587 lb).

View attachment 890908

The R-2000 is an awfully small engine for a successful fighter in 1943.

 

[Jugman]

Curtiss tested a few radials in their XP-60 project

The XP-60A-1 was planned to have an R-2800-18 installed, but was canceled.

The XP-60C had an R-2800-53 installed.

The XP-60E had an R-2800-10 installed.

Following the various spin-offs of the P-40 is like going down a rabbit hole. So basically, the P-60 derived from the P-53, which came from the P-46, which was developed from a P-40.

Nitpick: The P-46 ( Model 86) was a completely new design.
Model 75 covers the P-36, XP-37, XP-40, and XP-42.
Model 80 was the rebuilt XP-37.
Model 81 was the YP-37.
Models 81A/B was the P-40-P-40C and Tomahawks.
Model 87 was the Kittyhawks and P-40D-P-40Q. This design was a stopgap that used the wings of the Model 81 with the fuselage planed for what became the Model 88.
Model 88 was P-53 same fuselage as the Model 87 with a new laminar wing and powered by a IV-1430 or improved V-1710.
Model 90 was P-60 & P-60D A Model 88 with some minor improvements and Merlin.
Model 95 was all other P-60s had a new fuselage.